Magnetic disk comprising a first carbon overcoat having a high SP3 content and a second carbon overcoat having a low SP3 content

ABSTRACT

A method for making a magnetic disk comprises forming first and second protective carbon layers on a magnetic layer. The first protective carbon layer is predominantly SP3 carbon. The second protective carbon layer comprises about 50% or less SP3 carbon. The second protective carbon layer is very thin, e.g. between 0.1 and 1.0 nm thick. A lubricant layer (e.g. a perfluoropolyether lubricant) is applied to the second protective carbon layer. The second protective carbon layer facilitates improved cooperation between lubricant and the disk.

BACKGROUND OF THE INVENTION

[0001] This invention pertains to methods for manufacturing magneticdisks comprising carbon protective overcoats and the resulting magneticdisks.

[0002]FIG. 1 illustrates in cross section a magnetic disk 10 in a diskdrive 12. Magnetic disk 10 comprises a substrate 14 (e.g. glass, glassceramic, or NiP-plated aluminum), an underlayer 16 (e.g. Cr, a Cr alloy,NiP, NiAl or other appropriate material), a magnetic layer 18 (e.g. a Coalloy), and a protective overcoat 20 (e.g. hydrogen-doped carbon,nitrogen-doped carbon, or carbon doped with both hydrogen and nitrogen).A lubricant layer 22 (e.g. perfluoropolyether) is applied to protectiveovercoat 20.

[0003] Magnetic disk 10 is mounted on a spindle that is rotated by amotor 24. A read-write head 26, mounted on a suspension 28, “flies”above the rotating disk. Head 26 comprises a slider including a hard A1₂O₃-TiC body 30 with a read-write element 32 formed on the trailing edgethereof. A carbon overcoat 34 is formed on the bottom surface (the airbearing surface) of head 26 for tribological purposes.

[0004] Magnetic layer 18 performs the function of storing data. Overcoat20 performs several functions:

[0005] a) It prevents corrosion of magnetic layer 18.

[0006] b) It is hard, and prevents mechanical damage of magnetic layer18.

[0007] c) It exhibits low static and dynamic friction.

[0008] d) It holds lubricant layer 22 on disk 10.

[0009] e) It prevents wear of disk 10.

[0010] Industry has devoted a large amount of time and effort trying tofomi appropriate carbon films to be deposited on magnetic disks asprotective layers. For example, F. K. King, “Datapoint Thin Film Media”,IEEE Trans. Magn., July 1982, discuses sputtering carbon on a magneticdisk. U.S. Pat. No. 5,045,165, issued to Yamashita, discusses sputteringa hydrogen-doped carbon film on a magnetic disk to prevent wear andcorrosion. Yamashita teaches that the hydrogen enhances wear resistanceof the carbon. European Patent Application EP 0 547 820 discussessputtering a nitrogen-doped carbon film on a magnetic disk. The '820application states that the nitrogen reduces stress in the carbon, andreduces the likelihood that the carbon will delaminate from the disk.U.S. Pat. No. 5,837,357 discusses a magnetic disk comprising ahydrogen-doped carbon film covered by a nitrogen-doped carbon film. U.S.Pat. No. 5,232,570 also discusses sputtering carbon on the magnetic diskin the presence of nitrogen. Other references pertaining to carbonovercoats for magnetic disks include U.S. Pat. No. 5,855,746 and PCTPatent Application WO 99/03099. This list is by no means exhaustive.

[0011] Protective carbon overcoats for magnetic disks are typicallyformed by sputtering. Because of the way in which they are formed, theycomprise mostly SP2 carbon. Industry has been using such carbon filmsfor many years, and has considerable experience with these films. Thus,various types of lubricants have been developed which can be applied topredominantly SP2 carbon films to cause these films to exhibit lowfriction and stiction. (As used herein, the term “predominantly SP2carbon” means that of the carbon bonds in the film, more of those bondsare SP2 than any other type of bond. Similarly, “predominantly SP3carbon” means that of the carbon bonds in the film, more are SP3 thanany other type of bond.)

[0012] Recently, Komag (the assignee of the present invention) developeda new type of carbon overcoat comprising more than 70% SP3 carbon. Thistype of carbon overcoat is described by Wen Hong Liu et al. in U.S.patent application Ser. No. 09/298,107, filed on Apr. 22, 1999,incorporated herein by reference. The '107 carbon is deposited byapplying a novel voltage waveform to carbon sputtering targets. It hasbeen discovered that this carbon overcoat is extremely hard and scratchresistant.

[0013] There are other types of carbon overcoats that have high SP3contents. In particular, one can form a carbon film using chemical vapordeposition, ion beam deposition, or cathodic arc deposition. Weiler etat., “Deposition of Tetrahedral Hydrogenated Amorphous Carbon Using aNovel Electron Cyclotron Wave Resonance Reactor”, Applied PhysicsLetters, Vol. 72, No. 11, Mar. 16, 1998, discusses ion beam depositionof carbon. Kang, et al., “Evaluation of the Ion Bombardment Energy forGrowing Diamondlike Carbon in an Electron Cyclotron Resonance PlasmaEnhanced Chemical Vapor Deposition”, J. Vac. Sci. Technol. A. 16(4),July/August 1998, discusses using chemical vapor deposition to fonn acarbon film. J. Robertson, “Ultrathin Carbon Overcoats for MagneticStorage Technology”, TRIB-Vol. 9, Proceedings of the Symposium onInterface Technology Towards 100 Gbit/in², ASME 1999 discusses cathodicarc deposition. Other references include U.S. Pat. No. 5,476,691; Brown,“Vacuum Arc Ion Sources”, Rev. Sci. Instrum. 65(10), October 1994,Sanders, et al., “Coating Technology Based on the Vacuum Arc—a Review”,IEEE Transactions on Plasma Science, Vol. 18, No. 6, 1990; and Anders etal., Mechanical Properties of Amorphous Hard Carbon Films Prepared byCathodic Arc Deposition”, Mat. Res. Soc. Symp. Proc. Vol. 383, 1995.Japanese laid-open publication 62-183022 discusses using a plasma CVDprocess to make a carbon film on a magnetic disk. Weiler, Kang,Robertson, the '691 patent, Brown, Sanders, Anders, and the 62-183022references are incorporated herein by reference.

[0014] SP3 carbon has an atomic structure that differs from SP2 carbon.Accordingly, the behavior of SP2 carbon can be quite different from SP3carbon-sometimes to an unpredictably great extent.

[0015] As mentioned above, magnetic disk drive 12 contains magnetic disk10 with carbon protective overcoat 22 and lubricant 24 applied to thedisk. The disk substrate 14 is textured to minimize friction andstiction between disk 12 and read-write head 26. The disk/read-writehead interface constitutes a finely tuned tribological system designedto minimize static and dynamic friction and wear. The texturing of thedisk, the composition, deposition conditions and structure of carbonprotective overcoats 22 and 34, the other elements added to the carbonovercoats, the types of lubricants, the additives in the lubricants,lubricant application process and related parameters are determinedbased on exhaustive research to ensure that the disk drive can survive alarge number of on/off (contact-start-stop, or “CSS”) cycles. Changingone element in this tribological system call alter the behavior of theentire system. For example, if one were to replace a conventional typeof predominantly SP2 carbon with a different type of carbon, e.g. apredominantly SP3 carbon, that can completely change the behavior of thetribological system.

[0016] Merely by way of example, it has been discovered that when onetries to use the '107 type carbon and a perflouropolyether lubricantsuch as Z-dol (manufactured by Montedison Co. of Italy) mixed with anX1P additive, for reasons not well understood, the resulting disks tendto fail glide tests. This is particularly interesting and unexpected,since the lubricant thickness is only about 3 nm, whereas the glidetesting is performed at a glide height of about 1 microinch, or about 25nm. Thus, it is highly unexpected that the lubricant could interact withthe carbon film in such a way as to cause a failure in a glide testwhere the glide height is eight times the lubricant thickness.

[0017] Certain forms of high SP3 carbon formed by chemical vapordeposition have been found to exhibit other problems, i.e. sensitivityto certain types of contaminants.

SUMMARY

[0018] A method in accordance with the invention comprises depositingfirst and second carbon layers on a magnetic disk and then applying alubricant to the magnetic disk. In one embodiment, the first carbonlayer is predominantly SP3 carbon. The first layer can have 70% orgreater SP3 bonding. The second layer comprises less than or equal to50% SP3 bonding. The second layer can be extremely thin, e.g. a flashlayer of having a thickness between 0.1 and 1 nm. The lubricant can be aperfluoropolyether lubricant.

[0019] Of importarice, the high SP3 content protective layer isextremely hard, and resists wear and scratching. Because the secondprotective layer is so thin, it does not add substantially to theseparation of the magnetic film within the disk and the read-write head.

[0020] It has further been discovered that although the secondprotective layer is extremely thin, the properties of the secondprotective layer control the manner in which the lubricant cooperateswith the disk. In particular, although the second carbon layer is only0.1 to 1 nm thick, the lubricant bonds with, and adheres to the secondcarbon layer in the same way that the lubricant would cooperate with thecarbon on a conventional magnetic disk. The second carbon layer can maskany deleterious effects that the high SP3 content of the first carbonlayer would otherwise have on the disk's interaction with the lubricant.

[0021] As mentioned above, the first and second carbon layers havedifferent structures. Because the first carbon layer has mostly SP3bonds, it has a density greater than about 2.1 grams/cc, and typicallyabout 2.5 grams/cc. In contrast, the second carbon layer has a lowerdensity, e.g. less than about 2.1 grams/cc, and typically 1.8 grams/cc.

[0022] The first carbon layer has a refractive index that is greaterthan 2.0, and typically about 2.1. The second carbon layer has a lowerrefractive index than the first carbon layer, less than about 2.0 andtypically about 1.8.

[0023] In one embodiment, the first carbon layer has a lower surfaceenergy than the second carbon layer. (One way of measuring the surfaceenergy is by a water contact energy test. The difference in watercontact angle between the first and second carbon layers can be greaterthan 3 degrees and in one embodiment, greater than about 5 degrees. Thisdifference in water contact angle is typically less than about 8degrees.) In accordance with another aspect of the invention, a new typeof carbon overcoat is introduced into the manufacturing process for amagnetic disk without requiring the exhaustive optimization andreengineering that normally occurs when one makes a change to one of theelements of the tribological system of the disk and read-write head. Inaccordance with this aspect of the invention, a process formanufacturing a magnetic disk initially comprises the steps of:

[0024] a) providing a structure comprising a substrate with a magneticlayer thereon;

[0025] b) depositing a first carbon overcoat on the magnetic layer (e.g.a predominantly SP2 carbon overcoat formed by sputtering); and

[0026] c) applying a lubricant layer on the protective overcoat.

[0027] A method in accordance with the invention comprises replacing thestep of depositing the first carbon overcoat with the step of providinga carbon overcoat having characteristics that are different from thoseof the first overcoat (e.g. an overcoat with predominantly SP3 carbon),followed by the step of a depositing a very thin layer of carbon usingthe same or substantially the same deposition conditions as those usedto form the first carbon overcoat. For example, the process gascomposition, pressure, and flow rate are the same or substantially thesame. The substrate bias and temperature can be the same orsubstantially the same. Thus, the top surface of the magnetic disk,comprising the very thin layer of carbon, cooperates with the lubricantin substantially the same way as the above-mentioned first layer ofcarbon. Therefore, it is not necessary to do the substantial testing andengineering work that would otherwise need to be done if one simplyreplaced the first carbon overcoat with a predominantly SP3 carbonovercoat.

[0028] The predominantly SP3 carbon overcoat can be formed using themethod of the '107 patent, or it can be deposited by CVD or cathodic arcdeposition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 illustrates in cross section a magnetic disk driveconstructed in accordance with the prior art.

[0030]FIG. 2 illustrates in cross section a magnetic disk constructed inaccordance with the present invention.

DETAILED DESCRIPTION

[0031] A process in accordance with the present invention comprises thefollowing steps. First, a substrate 100 (FIG. 2) is provided. Thesubstrate can be glass, glass ceramic, NiP-plated aluminum or othersubstrate material. Substrate 100 is then textured, e.g. usingmechanical, laser or chemical techniques. (Such techniques are wellknown in the art.) One or more underlayers 102 (e.g. Cr, a Cr alloy,NiP, NiAl or other material) is deposited, e.g. by sputtering, ontosubstrate 100. Underlayer 102 can be about 10 to 30 nm thick.

[0032] One or more magnetic alloy layers 104 (e.g. a Co or Fe alloy) isdeposited, e.g. by sputtering, onto underlayer 102. Magnetic layer 104can be about 15 nm thick. In one embodiment, underlayer 102 and magneticalloy layer 104 are formed using the method and materials described inU.S. patent application Ser. No. 08/874,753, filed by Bertero et al. onDec. 4, 1997 and incorporated herein by reference.

[0033] A first overcoat 108 a having a relatively high SP3 content isdeposited on magnetic alloy layer 104. Overcoat 108 a is hard, and has,for example, about 70% or more SP3 carbon, and typically about 80% ormore SP3 carbon, e.g. as measured by the reflection energy lossspectrometer (REELS) technique. (The REELS technique is described byHsiao-chu Tsai et al. in “Structure and Properties of Sputtered CarbonOvercoats on Rigid Magnetic Media Disks”, J. Vac. Sci. Technol. A6(4),July/August 1988, incorporated herein by reference.) Overcoat 108 aminimizes wear, mechanical damage and corrosion of the disk. Overcoat108 a is typically about 2 to 5 nm thick. In. one embodiment, overcoat108 a is formed using the sputtering method described in U.S. patentSer. No. 09/298,107, filed by Wen Hong Lieu et al. on Apr. 22, 1999. Inanother embodiment, layer 108 a can be formed by chemical vapordeposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD).During PECVD, a hydrocarbon gas such as ethylene or acetylene isintroduced into the deposition chamber and caused to decompose, e.g. bythe application of electrical energy to the chamber. This results in thedeposition of a hydrogen-doped carbon film on the magnetic disk.

[0034] Overcoat 108 a can be formed by other techniques, e.g. cathodicarc deposition or ion beam deposition (IBD), e.g. as described in theabove-incorporated references.

[0035] A second overcoat 108 b is formed on and continuously coversfirst overcoat 108 a, e.g. by sputtering. Second overcoat 108 b is anextremely thin “flash” layer, e.g. 0.1 to 1.0 nm thick. (As mentionedabove, this flash layer 1.08 b cooperates with a subsequently depositedlubricant layer. As used herein, the term “flash” layer means a layer ofsufficient thickness to adequately cooperate with the lubricant layer sothat the lubricant functions properly, but not substantially thickerthan that.) Overcoat 108 b has a much lower SP3 content than overcoat108 a, e.g. less than or equal to about 50%. In one embodiment, the SP3content is between 40 and 50%. Because of the difference in thestructures of overcoats 108 a and 108 b, they have differentcharacteristics. In one embodiment, carbon 108 a has a density of about2.5 grams/cc, as measured by XRR (x-ray reflectivity). Carbon 1.08 b hasa density of 1.8 grams/cc. Carbon 108 a has a refractive index, asmeasured by an ellipsometer, of 2.1, whereas carbon 108 b has arefractive index of 1.9.

[0036] In one embodiment, carbon 108 b is formed by sputtering using aprocess gas comprising an inert gas such as argon mixed with nitrogen.(Optionally, hydrogen can be included in the process gas.) The gaspressure is between 2 and 10 mTorr, typically between 4 and 9 mTorr, andpreferably between 6 to 9 mTorr. The argon flow rate is 50 to 90 SCCM,and the nitrogen flow rate is 4 to 10 SCCM. In some embodiments, bias isapplied to the substrate, but in other embodiments, bias is not appliedto the substrate. The power density is 1 to 2 W/cm². The deposition rateof carbon layer 108 b is typically substantially less than thedeposition rate for carbon layer 108 a. In particular, the depositionrate for carbon layer 108 a is typically between 0.1 and 2 nm/second,and preferably between 0.5 and 1 nm/second.

[0037] After carbon layer 108 b is fonned, a lubricant layer 110 isapplied to the disk. The lubricant can be a perfluoropolyetherlubricant. An example of such a lubricant is Fomblin Z-dol, sold byMontedison Co. of Italy. An additive can be added to this lubricant. Anexample of such an additive is polyphenoxycyclotriphosphazene, describedU.S. Pat. No. 5,587,217, issued to Chao et al., incorporated herein byreference. An additive sold under the trade name X1P, manufactured byDow Chemical Corp. of Midland, Mich. can be used. The lubricant can beapplied to the disk by dipping the disk in a room temperature bathcomprising a mixture of the Fomblin Z-dol and X1P. The speed at whichthe disk is dipped into the lubricant bath can be 1 to 2 mm/minute.Optionally, after the dipping process, the lubricant can be subjected toa baking process. The thickness of the lubricant and additive on thedisk is about 3.2 nm, out of which about 3 nm is Z-dol, and 0.2 nm isX1P as measured by the FTIR technique.

Formation Of Carbon Layer 108 a by Sputtering

[0038] As mentioned above, carbon layer 108 a can be formed using thetechnique described in the '107 application. During one embodiment ofthis method, a graphite sputtering target us used. The process gascomprises argon, hydrogen and nitrogen. The argon gas flow is 50 to 70SCCM, the nitrogen gas flow is 0.5 to 2.0 SCCM and the hydrogen gas flowis 15 to 30 SCCM. The power density is about 1 KW/100 cm², i.e. about 10W/cm². Bias supply to the substrate is minus 100 to minus 200 volts.Magnetron sputtering can be employed. Optionally, the substrate can beheated. In one embodiment, sputtering apparatus such as an Anelva C-3010sputtering apparatus can be used. Other apparatus, such as an Ulvacsputtering machine can also be used. A power supply, e.g. an RPG modelpulse power supply made by ENI Inc. of Rochester, N.Y. can be used.

[0039] As described in the '107 Application, a unique voltage waveformis applied to the sputtering target. This waveform comprises an initialpositive potential portion, e.g. a portion that can be about 300 volts.Thereafter, a negative voltage is applied to the target. The negativeportion of the waveform typically comprises a negative pulse followed bya steady state negative voltage. The negative pulse can have two orthree times the magnitude of the steady state negative voltage. It isbelieved that the large negative swing in the voltage applied to thetarget momentarily causes a high deposition rate and carbon atoms canhave much higher energy than they would have during conventionalsputtering. It is believed that this voltage waveform causes the newprotective overcoat to have a greater SP3 content, and exhibit greaterhardness, than typical sputtered carbon films. The waveform applied tothe sputtering target can have a frequency between about 50 ktz and 250kiz.

Formation of Carbon Layer 108 a by CVD

[0040] In one embodiment, carbon layer 108 a is formed by CVD (typicallyplasma-enhanced CVD), or PECVD) by applying 1000 Watts to the CVDapparatus, with a substrate bias of 300V and a process gas of C₂H₄(ethylene) flowing at a rate of 150 SCCM. The pressure in the depositionchamber is typically between about 20 to 40 mTorr. The process time isabout 5 seconds, and results in 5 nm of predominantly SP3 carbon. Thesubstrate is not heated in this particular example of a CVD process. Thedetails for this process are merely exemplary. Other carbon-containingprocess gases and other parameters can also be used.

Modification of a Pre-existing Manufacturini Process

[0041] As mentioned above, a read-write head and magnetic disk form acarefully engineered tribological system designed to minimize frictionand stiction between the read-write head and the disk, minimize wear,and maximize the number of contact-start- stop (CSS) cycles that thedisk drive can survive. A great amount of engineering effort is requiredto accomplish these goals. This engineering effort includes:

[0042] a) Providing an appropriate disk texture having texture featuresof an appropriate size, shape and areal density.

[0043] b) Providing an appropriate protective overcoat composition (bothon the disk and the read-write head). This involves developing anappropriate composition, thickness and morphology and selecting adeposition process for the overcoat (e.g. CVD, sputtering, cathodic arcdeposition or IBD). This also requires determining an appropriateprocess gas composition, a flow rate for each component of the processgas, process gas pressure, substrate bias and substrate temperature.

[0044] c) Providing a lubricant composition, thickness and applicationtechnique. This also involves selecting additives for the lubricant(including selecting the concentration of the additives), and developingappropriate lubricant application parameters. (For example, for adipping process, this includes selecting the rate at which the disk isdipped into and withdrawn from the lubricant bath and the bathtemperature.)

[0045] Relacing one type of protective overcoat on the disk with anotherprotective overcoat can have a deleterious effect on the rest of thetribological system. For example, providing a new carbon overcoat on thedisk may cause the disk to fail to cooperate properly with thelubricant.

[0046] In accordance with one embodiment of the invention, a method isprovided for altering a magnetic disk manufacturing process. The processinitially comprises one or more of the steps of:

[0047] a) providing a substrate (e.g. a glass substrate, a glass ceramicsubstrate, a NiP-coated aluminum substrate, or other appropriatesubstrate material);

[0048] b) providing an underlayer on the substrate (e.g. Cr, a Cr alloy,NiP, NiAl, or other appropriate underlayer deposited by sputtering);

[0049] c) providing a magnetic layer on the underlayer (e.g. a sputteredCo or Fe alloy);

[0050] d) providing an initial protective overcoat on the substrate(e.g. a carbon film sputtered in the presence of nitrogen and/orhydrogen);

[0051] c) applying a lubricant to the protective overcoat (e.g. aperfluoropolyether lubricant applied by dipping.

[0052] Merely by way of example, the process described in theabove-incorporated '753 Bertero application can be used to form theunderlayer and magnetic layer. The protective overcoat can be formed bysputtering using the same sputtering conditions as those described forcarbon layer 108 b above. (In such an embodiment, the power applied tothe deposition chamber is typically greater than the above-mentioned 1to 2 W/cm² in order to obtain an appropriately high deposition rate.)The lubricant can be the above-mentioned Z-dol-X1P mixture applied bydipping, having a total thickness of about 32 nm

[0053] In accordance with this method, the step of depositing theprotective overcoat is replaced with the step of:

[0054] a) depositing a first, predominantly SP3 carbon overcoat on themagnetic layer; and

[0055] b) depositing a second carbon. overcoat on the first carbonovercoat.

[0056] The first, predominantly SP3 carbon overcoat can be depositedusing the deposition techniques and conditions described above forcarbon layer 108 b. The first carbon overcoat can be about 2 to 5 nmthick. The second carbon overcoat can be deposited by sputtering usingthe same or substantially the same conditions (e.g. the same orsubstantially the same process gas composition, flow rates for thevarious components of the process gas and process gas pressure) as forthe initial protective overcoat that is being replaced. The substratebias and/or substrate temperature can also be the same or substantiallythe same during deposition. (Typically, the power applied to thesputtering apparatus during deposition of the second carbon overcoat isless than the power used to deposit the initial protective overcoat.This facilitates a slower deposition rate for the second carbonovercoat.) Of importance, the second carbon overcoat has the same orsubstantially the same composition (including the same or substantiallythe same hydrogen and/or nitrogen content) and/or morphology (e.g. SP2and SP3 content) as the initial protective overcoat. Further, the secondcarbon overcoat cooperates with the lubricant layer in the same orsubstantially the same way as the initial protective overcoat. Thus,even though the initial protective overcoat is being replaced with adual layer structure comprising mostly SP3 carbon having a structurethat differs from the initial protective overcoat, the second carbonovercoat masks this mostly SP3 carbon, and provides a continuous carbonsurface that behaves and cooperates with the lubricant and/or othercomponents of the system (e.g. texture, slider surface, etc.) in thesame way as the initial protective overcoat. Thus, one can replace theinitial protective overcoat with this new, mostly SP3 carbon, withouthaving to engage in substantial reengineering of the head-disktribological system.

Industrial Application

[0057] A disk constructed using a method in accordance with the presentinvention is typically incorporated into a disk drive. The disk iscoupled to a motor via a spindle. The motor rotates the disk rapidly,while a read-write head “flies” above the disk drive. The read-writehead is held in place by a suspension.

[0058] While the invention has been described with respect to specificembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. For example, the process gas used to form layer 108 b caninclude between 0 and 20% nitrogen, 0 and 20% hydrogen in addition to aninert gas. In some embodiments, the SP3 content of layer 108 b isbetween 30 and 60%, but still substantially less than the SP3 content oflayer 108 a. The various layers (102 to 110) can be formed on one orboth sides of substrate 100. Accordingly, all such changes come withinthe present invention.

We claim:
 1. A method for making a magnetic disk comprising the stepsof: depositing a first carbon layer on said disk, said first carbonlayer comprising predominantly SP3 carbon; and depositing a secondcarbon layer on said disk, said second carbon layer comprising about 60%or less SP3 carbon, the SP3 content of the second carbon layer beingless than the SP3 content of the first carbon layer.
 2. Method of claim1 wherein the second carbon layer comprises less than about 50% SP3carbon.
 3. Method of claim 2 wherein the second carbon layer comprisesmore than about 30% SP3 carbon.
 4. Method of claim 1 wherein said secondcarbon layer has a thickness less than or equal to about 1 nm.
 5. Methodof claim 1 wherein said second carbon layer is between 0.1 and 1 nmthick.
 6. Method of claim 1 farther comprising a lubricant layer. 7.Method of claim 1 wherein the second carbon layer is formed bysputtering and the first carbon layer is formed by CVD, PECVD, IBD orcathodic arc deposition.
 8. Method of claim 1 wherein the first andsecond carbon layers are formed by sputtering.
 9. Method of claim 8wherein said depositing of said first carbon layer comprises: applying avoltage to a sputtering target, said sputtering target comprisingcarbon, said voltage being applied by a power supply in the form ofpulses, said pulses comprising at least a first portion and a secondportion, the voltage applied during said second portion being morenegative than that applied during said first portion, wherein a firstsub-portion of said second portion is more negative than a secondsub-portion of said second portion.
 10. A magnetic disk comprising: asubstrate; a magnetic layer formed on said substrate; a first carbonlayer formed on said magnetic layer, said first carbon layer comprisingpredominantly SP3 carbon; and a second carbon layer formed on said firstcarbon layer, said second carbon layer comprising about 60% or less SP3carbon, the SP3 content of said second carbon layer being less than theSP3 content of the first carbon layer.
 11. Disk of claim 10 wherein thesecond carbon layer comprises less than 50% SP3 carbon.
 12. Disk ofclaim 10 wherein said wherein said second carbon layer is a flash carbonlayer.
 13. Disk of claim 13 wherein said second carbon layer is between0.1 and 1.0 nm thick.
 14. A method for modifying a manufacturingprocess, said manufacturing process comprising providing a carbon-basedprotective overcoat on a magnetic disk using a set of parameters, saidmethod comprising modifying said process such that instead of providingsaid carbon-based protective overcoat on said magnetic disk using saidset of parameters, the following acts are performed: depositing a firstcarbon layer on said magnetic disk, said first carbon layer having anSP3 content of at least about 70%; and depositing a second carbon layerusing substantially said set of parameters, said second carbon layerbeing less than or equal to about 1.0 nm thick.
 15. Method of claim 14wherein said first carbon layer has a thickness between 2 and 5 nm. 16.Method of claim 14 wherein said depositing of said second carbon layercomprises sputtering said second carbon layer in a sputtering chamberand said parameters include the composition and pressure of the gas inthe sputtering chamber.
 17. Method of claim 14 wherein said parametersinclude the substrate temperature and bias voltage.
 18. Method of claim14 wherein said second carbon layer has a thickness greater than orequal to about 0.1 nm.
 19. Method of claim 14 wherein said first carbonlayer comprises at least one material selected from the group consistingof nitrogen and hydrogen.
 20. Method of claim 14 wherein said secondcarbon layer comprises at least one material selected from the groupconsisting of nitrogen and hydrogen.
 21. Method of claim 14 wherein saidsecond carbon layer comprises less than 60% SP3 carbon.
 22. A method formodifying a manufacturing process, said manufacturing process comprisingproviding a carbon-based protective overcoat on a magnetic disk using aset of parameters, said method comprising modifying said process suchthat instead of providing said carbon-based protective overcoat on saidmagnetic disk using said set of parameters, the following acts areperformed: depositing a first carbon layer on said magnetic disk, saidfirst carbon layer comprising predominantly SP3 carbon; and depositing aflash layer of carbon using said set of parameters.
 23. Method of claim22 wherein said first carbon layer comprises about 70% or more SP3carbon.
 24. Method of claim 22 wherein said flash layer has a thicknessless than about 1 nm.
 25. Method of claim 22 wherein said flash layercomprises at least one material selected from the group consisting ofhydrogen and nitrogen.
 26. Method of claim 22 wherein said first carbonlayer comprises at least one material selected from the group consistingof hydrogen and nitrogen.
 27. A method for modifying a manufacturingprocess, said manufacturing process comprising providing a carbon-basedprotective overcoat on a magnetic disk, said method comprising modifyingsaid process such that instead of providing said carbon-based protectiveovercoat on said magnetic disk, the following acts are performed:depositing a first carbon layer on said magnetic disk, said first carbonlayer comprising predominantly SP3 carbon; and depositing a secondcarbon layer that cooperates with lubricant with substantially the sameeffectiveness as said protective overcoat.
 28. Method of claim 27wherein said first carbon layer has an SP3 content of about 70% or more.29. Method of claim 27 wherein said second layer is less than about 12nm thick.
 30. Method of claim 27 wherein said second carbon layer hassubstantially the same SP3 content as said protective overcoat. 31.Method of claim 27 wherein said second carbon layer has substantiallythe same density and refractive index as said protective overcoat. 32.Method of claim 27 wherein said second carbon layer has substantiallythe same surface energy as said protective overcoat.
 33. Method of claim27 wherein said second carbon layer has substantially the same chemicalproperties as said protective overcoat.
 34. Method of claim 27 whereinsaid second carbon layer comprises at least one material selected fromthe group consisting of hydrogen and nitrogen.
 35. Method of claim 27wherein said first carbon layer comprises at least one material selectedfrom the group consisting of hydrogen and nitrogen.
 36. Method of claim27 wherein said second carbon layer is a flash layer.
 37. Method ofclaim 27 wherein without said second carbon layer, the cooperationbetween said lubricant layer on said first carbon layer would be such asto tend to cause said disk to fail a glide height test, and wherein saidsecond carbon layer permits said magnetic disk to pass said glide heighttest.
 38. Method of claim 27 wherein said glide height test tests saiddisk at a height of about 1 microinch.
 39. Method of claim 27 whereinsaid first carbon layer has a greater SP3 content than said secondcarbon layer.
 40. A method for modifying a manufacturing process, saidmanufacturing process comprising providing a carbon-based protectiveovercoat on a magnetic disk, said carbon-based overcoat comprising onecomponent of a head-disk interface, said method comprising modifyingsaid process such that instead of providing said carbon-based protectiveovercoat on said magnetic disk, the following acts are performed:depositing a first carbon layer on said magnetic disk, said first carbonlayer comprising predominantly SP3 carbon; and depositing a secondcarbon layer that cooperates with at least one second component of saidhead-disk interface with substantially the same effectiveness as saidprotective overcoat.
 41. The method as described in claim 39 whereinsaid second component of said head-disk interface comprises one or moreof a lubricant applied above said second carbon layer, a texture formedon said disk; and a slider having a read element thereon.